I love mjecke's Karaoke Delay idea, a panel that converts a dirt cheap delay module to eurorack. I wanted to try to find a use for the extra 'mod' input, the unused 'AUX' pot, and make some general improvements for Eurorack.
The delay module has a 33:1 gain section, meant for microphones. I changed out the 33k resistor for a 1k resistor. This keeps the gain pot functional, but lowers the max gain to 1:1, and still has an input buffer. If you want a bit more gain at max, a 2K2 would be a good idea. The resistor needed to be replaced is the bottom of the two directly to the left of the TL072 opamp.
There is a 3 pin connector on the right labelled Lin, Rin, and ground. This pair of inputs is attenuated by the AUX pot, so I used this input for the CV control.
I removed the 220pf capacitor for the MIC2 input, because it was in the way of my jacks. I'm not using the MIC2 input anyway, so this has no effect on functionality.
Input is wired to the empty pad on MIC1, Output is a long wire going to the top OUT spot. The MOD input is wired to the LIN pad.
An addition of a single 1K resistor feeds the incoming CV to the TIME control. I placed this resistor on the top side of the board and connected the right leg of the bottom 33k resistor to the right leg of this 10K resistor.
The 33k resistor carries the aux signal through to the output of the module. This signal is not effected by the delay, and is AC coupled, so slow CVs will not pass through, but using audio as a CV source will result in that signal being present on the output. Cut out this bottom 33k resistor (but leaving the new 1K) if you don't want your modulator to be passed through to the output.
The final build looks very neat and tidy, no components or wiring on the bottom side, all inputs and knobs have functions, and the entire modification is very simple to do. All in all, I'm quite happy with the result.
Remove 2 white connectors, screw terminal, and 2 1/4" inputs
Fit panel on board and tighten down nuts. I had to clip the tabs off the pots to get the panel flush.
Install your 3 1/8" jacks. Ground them to the ground pads on the 1/4" jacks, or on the bottom 3 pin connector.
Install a 10 pin box connector, clip off 7 of the legs so the box connector can sit flush. It doesn't matter which way around the box connector goes.
Remove 33K resistor near TL072, replace with 1K or 2K2 (2K2 for a boost in volume at max)
Remove 33K below PT2399, and install 1K to bridge the CV to the Time control
Install wires for input, output, and mod
2 x 1K resistors, or 1 x 1K and 1 x 2K2
3 x 1/8" jacks
6" of wire
IDC Box Connector